Field of the Invention
The present invention relates to a deformable mirror and a method for manufacturing the same.
Description of the Related Art
A deformable mirror is an optical device and usable as a wavefront aberration correction device in adaptive optics. The deformable mirror is thus expected to be applicable to various uses in the optical field including a funduscope and an astronomical telescope. U.S. Pat. No. 7,929,195 discloses a deformable mirror in which a deformable layer having a certain film thickness and including a reflective layer is connected to a plurality of electrostatic actuators via a plurality of coupling portions. The deformable mirror is formed into an appropriate shape by driving the electrostatic actuators so that multiple portions of the deformable layer connected to the actuators are individually pulled substantially downward in the vertical direction. Japanese Patent Laid-Open No. 2008-40304 discloses a deformable mirror used in an optical pickup device of an optical disc information input-output device. Specifically, a deformable mirror connected to actuators via protrusions formed on the mirror substrate is disclosed.
In the deformable mirror disclosed in U.S. Pat. No. 7,929,195, portions of the deformable layer around the coupling portions are deformed at a smaller angle than an ideal shape due to the flat shape of the coupling portions, whereby the surface shape of the deformable mirror deviates from an ideal surface shape.
For example, FIG. 6 illustrates simulation results of deformed mirror shapes of models having a mirror shape similar to those according to U.S. Pat. No. 7,929,195, when a plurality of actuators are driven so as to form an ideal surface shape indicated by the line x, where the simulated shapes are represented by the lines b and c. The line b represents the result obtained when the mirror thickness is 1.2 μm and the line c represents the result obtained when the mirror thickness is 3.0 μm. FIG. 6 shows that the mirror shape according to U.S. Pat. No. 7,929,195 deviates from an ideal surface shape to a large degree regardless of the thickness of the mirror substrate. Thus, a wavefront aberration optical system including such a deformable mirror is unable to completely correct aberration due to the deviation of the surface shape from the ideal surface shape and requires improvement in optical characteristics such as resolving power.
Also in the deformable mirror disclosed in Japanese Patent Laid-Open No. 2008-40304, a deformable portion of the mirror substrate has a uniform thickness except for the protrusions connected to the actuators. Consequently, similarly to the deformable mirror disclosed in U.S. Pat. No. 7,929,195, the shape of the mirror substrate deviates from an ideal surface shape due to a decrease in amount of deformation around the portions connected to the actuators.